The first semester at our school was the hardest. I'm not even sure how to give advice other than to say prepare for the most difficult thing you've ever done. Unrelated to the academics, be nice to your colleagues. I could not have made it through the first year without the many encouraging, thoughtful friends I made. The students who came in gunning for the top at anyone's expense tend to be disliked and isolated.
Every metaphor you've heard about medical school is true. It is like drinking from a fire hydrant. Content is not more difficult than an undergrad upper level science course; but, you will cover a semester worth of that class in 2-3 weeks. So much of my success in medical school has come from developing new study habits. I used to print out lecture notes and copy ever word the professor said. This is not a reasonable approach. Now, all I take into lecture with me is paper and a pen. I make an outline of the lecture and write down anything that I've never heard before. Go through the given out notes a couple times. Then try to recondense the notes in your own words. The weekend before an exam, you should be studying your condensed notes.
Anyways, medical school is a privilege. And don't ever forget how lucky you are to be selected to attend. It will be difficult, but no one has ever said that it's easy. Best of luck.